The pattern of violence that heralded the death of toddler JJ Lawrence coincided with murder-accused Joel Lofflley coming into his life, the Crown has said in closing statements to the court.

Prosecutor Phil Hamlin told the High Court in Auckland today that JJ began receiving broken arms and suspicious bruises when Loffley moved in with his mother Josephine Lawrence.

The Crown case is that on the morning of November 14, 2011, Loffley struck JJ at their Orakei, Auckland, home while Lawrence was out of the house.

Doctors said the injuries to the boy's abdomen looked like they had been caused by a horse's kick or a car crash - his pancreas and liver had been pushed back onto his spine with such force they split in half.

JJ was also found to have cannabis in his system, which Lawrence said Loffley used to give to the boy.

Hamlin asked the jury who was violent and controlling in the relationship and who had motive to kill JJ.

Anticipating the defence case he asked: "Why on Earth would this mother want to kill her child?"

Hamlin pointed to lies Loffley told that distanced himself from any harm to JJ, including telling police one of the boy's broken arms happened when he was staying with family. Josephine Lawrece testfied that Loffley had admitted he may have caused it.

Loffley found JJ in his bed not breathing but Hamlin asked why Loffley had gone to check on him at all.

Loffley had just returned from buying alcohol and was only going inside to get some soft drink for his vodka.

Instead, he went upstairs and discovered JJ not breathing.

Only the killer would have known JJ was in distress, Hamlin said; JJ's mother sat obliviously watching a movie in the next room as she did not know anything was amiss.

Loffley has maintained JJ fell off a bed and his legs went over his head when he hit the ground.

Hamlin said this was Loffley's "big lie" - the killer would have seen JJ's immediate distress but the only outward sign to be explained away was a graze to the boy's chin.

His story of the fall kept changing and no-one else in the house heard the fall, Hamlin said.